This invention relates to a high frequency field-effect transistor necessitating no epitaxial and isolation regions and being adapted for various integrated circuits. Recently, an improved field effect transistor having a channel length which is determined by the difference between diffusion distances of impurities into the substrate from the same selection edge of a selective diffusion mask has been proposed. As the channel length is determined by the difference of the diffusion length measured from the same position and not directly affected by photoengraving technique, excellent super-high-frequency characteristics can be obtained, because said channel length can be made to be shorter by one order of magnitude than the minimum value (several .mu.) of a transistor of conventional structure. However, this improved transistor requires indispensably the use of the so-called epitaxial growth technique and isolation diffusion process in order to be made in an integrated circuit.
Furthermore, excellent integrated circuits having high performance have not yet been obtained because it has been impossible to combine skillfully a transistor having excellent high-frequency characteristics and a depletion-type transistor having characteristics which are substantially equivalent to constant-current characteristics.